Method for drilling wells

ABSTRACT

Drilling of wells in subfreezing environments is conducted by using a fluid which contains a major amount of an aqueous medium such as sea water or fresh water, a heteropolysaccharide produced by the action of bacteria of the genus Xanthomonas, an oxygenated hydrocarbon dispersant which may be a polyhydric alcohol such as ethylene glycol and, optionally, an alkaline medium to provide a desired pH, the polyhydric alcohol aiding in the dispersion of the heteropolysaccharide in the aqueous medium and acting as a freezing point depressant of the drilling fluid.

Unite States Patent [72] Inventor Stanley A. Christman Los Angeles,Calif. [21] Appl. No. 41,657 [22] Filed May 27, 1970 [45] Patented Jan.11, 1972 [73] Assignee Esso Production Research Company [54] METHOD FORDRILLING WELLS 21 Claims, No Drawings [52] US. Cl 175/65, l66/DIG. l,252/8.5 A

[51] lnt.Cl E2lb 21/04 [50] Field of Search 175/65, 72;

166/D1G. l, 246; 252/85 R, 8.5 A, 8.5 C

[56] References Cited UNITED STATES PATENTS 3,000,790 9/1961 Jeanes eta1 175/65 UX 3,179,528 4/1965 l-lolmgren et al. l66/DlG. 1 3,198,2688/1965 Lindblom et al.... 166/246 X 3,243,000 3/1966 Patton et a1 175/653,251,768 5/1966 Walker 175/65 UX 3,305,016 2/1967 Lindblom et a1.175/65 X 3,319,715 5/1967 Parks 175/65 X OTHER REFERENCES Kelly, AlaskanOperators Solve Tough Drilling Problems, World Oil, December 1968, pp.63- 67.

Primary Examiner-Stephen .l. Novosad Attorneys-Thomas B. McCulloch,Melvin F. Fincke, John S. Schneider, Sylvester W. Brock, .lr., TimothyL. Burgess and Kurt S. Myers ABSTRACT: Drilling of wells in subfreezingenvironments is conducted by using a fluid which contains a major amountof an aqueous medium such as sea water or fresh water, aheteropolysaccharide produced by the action of bacteria of the genusXanthomonas, an oxygenated hydrocarbon dispersant which may be apolyhydric alcohol such as ethylene glycol and, optionally, an alkalinemedium to provide a desired pH, the polyhydric alcohol aiding in thedispersion of the heteropolysaccharide in the aqueous medium and actingas a freezing point depressant of the drilling fluid.

METHOD FOR DRILLING WELLS BACKGROUND OF THE INVENTION 1. Field of theInvention The present invention is primarily directed to fluids for usein wells such as oil and gas wells where subfreezing conditions areencountered. More particularly, the invention is directed to acomposition useful in Arctic and other subfreezing environments, amethod of preparing the fluid, and a method for drillinga well with afluid in subfreezing environments. In its more specific aspects, theinvention is concerned with an aqueous fluid containing dispersedtherein a heteropolysaccharide produced by the action of bacteria of thegenus Xanthomonas and an oxygenated hydrocarbon dispersant, whichresulting fluid has a reduced freezing point.

2. The Prior Art It has been known heretofore to useheteropolysaccharides in drilling muds. It has also been known to usethese materials which have been cross-linked with a polyvalent metalcation. Drilling operations have been conducted in the Arctic withdrilling fluids containing heteropolysaccharides. While these operationsare improved to some extent by use of the heteropolysaccharides, due tothe environment, such as subfreezing atmospheric temperatures andpermafrost, even use of the heteropolysaccharide-containing muds presentproblems since it may be necessary and/or desirable to use the resultingfluid at a temperature below its normal freezing point. I-Ieretofore, ithas been known that the addition of an inorganic salt, such as sodiumchloride, may reduce the freezing point of a drilling fluid, butproblems result from difficulty in dissolving the salt into a coldaqueous medium, from limited freezing point depression, and from otheradverse effects of the salt on the drilling operation. Moreover,dispersion of the heteropolysaccharides into the aqueous medium is oftentroublesome because the hydrophilic nature of heteropolysaccharides maycause lumping which inhibits dispersion.

However, the difficulties encountered in making up theheteropolysaccharide-containing fluids are substantially and unobviouslyovercome or mitigated since it has been surprisingly discovered that anoxygenated hydrocarbon dispersant such as a polyhydric alcohol may beused as a slurrying or dispersing agent in making up the fluid, andfurthermore the polyhydric alcohol also acts as a freezing pointdepressant in the fluid which prevents the fluid from freezing when usedin such hostile environments or under such extreme subfreezingtemperature conditions. Thus, the polyhydric alcohol performs twofunctions in heteropolysaccharide-containing aqueous fluids.

SUMMARY OF THE INVENTION The present invention may be briefly describedand summarized as a fluid suitable for use in drilling oil and gas wellsand particularly oil and gas wells in subfreezing environments such asin the Arctic; the fluid comprising a major amount of an aqueous mediumwhich may be salt water, brine, fresh water, or a suspension ofcolloidal particles in water such as drilling mud. The fluid contains anamount of a heteropolysaccharide produced by the action of bacteria ofthe genus Xanthomonas on a carbohydrate within the range of about 0.05to about 5 percent by wt. of the aqueous medium. Also, the fluidcontains an amount of an oxygenated hydrocarbon dispersant within therange of about 1.0 to about 30 percent by wt. of the aqueous medium anda sufficient amount of an alkaline medium to provide a pH on the fluidwithin the range of about 8 to about 10.

The invention also may be briefly described and summarized as a methodof preparing the fluid in which the amount stated of theheteropolysaccharide produced by the action of the bacteria of the genusXanthomonas on a carbohydrate is added to the stated amount ofoxygenated dispersant; the amounts of oxygenated dispersant andheteropolysaccharide are agitated for a sufficient time within the rangeof about 0.25 to about 5 minutes to form a slurry or dispersion of theheteropolysaccharide and the oxygenated dispersant. The slurry is thenmixed with the aqueous medium and the same is agitated for a'time withinthe range of about 15 to 45 minutes to disperse the slurry in theaqueous medium. If desired, the heteropolysaccharide may be furtherdispersed by the addition of a sufi'rcient amount of an alkaline mediumto provide a pH within the range of about 8 to about 10.

The invention may also be described and summarized as embodying a methodof drilling a well, particularly in a subfreezing environment such as inthe Arctic, where atmospheric temperatures are below the freezing pointof water and/or where the permafrost may be encountered. In suchregions, it may be necessary and/or desirable to use this fluid attemperatures below 32 F. Also, a method is described for drilling a wellon rotating a drill bit to form a well bore and circulating in the wellbore a drilling fluid which is the composition of the present invention,and recovering from the well bore cuttings such that a clean well boreis provided. This is particularly important where gravel and otherunconsolidated materials are encountered.

VARIABLES OF THE INVENTION The polysaccharides employed in preparing thefluids of the invention are heteropolysaccharides produced by the actionof bacteria of the genus Xanthomonas on carbohydrates. Representativespecies of these bacteria which may be employed to produce theheteropolysaccharides include Xanthomonas begoniae, Xanthomonascampestris, Xanthomonas carotae, Xanthomonas corylina, Xanthomonasgummisudans, Xanthomonas hederae, Xanthomonas incanae, Xanthomonaslespedezae, Xanthomonas malvacarum, Xanthomonas halcicola, Xanthomonaspapavericola, Xanthomonas phaseoli, Xanthomonas pisi, Xanthomonastranslucens, Xanthomonas vasculorum and Xanthomonas vesicatoria. Studieshave shown that the production of the heteropolysaccharides is acharacteristic trait of members of the genus Xanthomonas but thatcertain species of the genus produce the polymers with particularefficiency. Species which are outstanding in this respect includeXanthomonas begoniae, Xanthomonas campestris, Xanthomonas incanae andXanthomonas pisi. These species are therefore preferred for thesynthesis of the heteropolysaccharides.

The heteropolysaccharides employed in the present invention are producedas described in US. Pat. No. 3,243,000 and may be used in amounts withinthe range from about 0.05 to about 5.0 percent by wt. of the aqueousmedium which may be sea water, other brine, fresh water or a drillingmud such as used in drilling oil and gas wells.-

The muds used in drilling oil wells, gas wells and similar bore holesare generally aqueous liquids containing clays or other colloidalmaterials in substantial quantities. These colloidal constituentscontribute to the viscosity and gel strength necessary for theentrainment and suspension of cuttings and weighting agents and assistin the formation of the filter cake needed for the reduction of fluidlosses to the surrounding subsurface strata. It has been shown thatexcessive viscosity has an adverse effect on the penetration ratesobtained and that substantially better rates can often be secured byeliminating the colloidal materials and using air, clear water or asimilar fluid of low viscosity in place of ordinary mud. This isgenerally practical only in shallow wells where weighted fluids are notrequired, where the gel strength and fluid loss properties are notcritical, and where no unusual hole conditions are apt to beencountered. Various mud formulations intended to permit thesatisfactory entrainment and suspension of solids and to provide therequired filter cake without adversely affecting the drilling rate havebeen suggested from time to time but have generally not been successful.These drilling muds may not be satisfactorily used in subfreezingenvironments because of the low temperatures encountered which may causedifficulties in circulation of the drilling mud and rotation of thedrill bit. In fact, subfreezing temperatures may solidify the mass.

The heteropolysaccharides are used in an amount within the range from0.05 to about 5.0 percent by wt. of the aqueous medium; a preferredrange is about 0.25 to 1.0 percent by wt.

The oxygenated dispersants employed in the present invention are used inan amount within the range of about 1.0 to about 30 percent by wt. ofthe aqueous medium, but a range of about 5 percent to about 20 percentby wt. is preferred.

The oxygenated dispersants may suitably be a polyhydric alcohol such asethylene glycol, diethylene glycol, triethylene glycol, propyleneglycol, glycerol, 1, S-pentanediol, and the like. Other oxygenateddispersants include the ketones with acetone being preferred. Methylethyl ketone and other water soluble ketones may be used. As examples ofother ketones may be mentioned diacetone alcohol, and the like. The lowmolecular weight aliphatic alcohols such as but not limited to methyl,ethyl, propyl, and isopropyl alcohols may also be used. Other usefuloxygenated dispersants include diethyl ether, ethyl acetate,formaldehyde and other aldehydes and the like. As a general rule,oxygenated dispersants which are soluble in water and have a molecularstructure similar to the structure of the heteropolysaccharide may beused as an oxygenated dispersant for the heteropolysaccharide in waterand also lower the freezing point of the composition.

The heteropolysaccharides employed in the present invention may be usedas such, but preferably the heteropolysaccharides are cross-linked.heteropolysaccharides in aqueous solutions are cross-linked with apolyvalent metal cation selected from Groups III through VIII of thePeriodic Table. Cross-linking agents employed are preferablywater-soluble trivalent chromium compounds such as chromium bromide,chromium chloride, chromium nitrate, basic chromium sulfate, chromiumammonium sulfate, chromium potassium sulfate, and the like. Products onthe market termed chrome-alum and organic chrome polymer give quitedesirable results. The reaction may be carried out with otherwater-soluble compounds which yield polyvalent metal cations in aqueoussolutions, such as aluminum chloride, ferric chloride, manganesedichloride, magnesium aluminum silicate and the like. While thesematerials may be used, they are less desirable because they are lesseffective than the water-soluble compounds of chromium referred toabove. The methods and amounts used for preparing the cross-linkedheteropolysaccharides are described in U.S. Pat. No. 3,243,000.

While the cross-linked heteropolysaccharides are preferred in thepractice of the present invention, the heteropolysaccharides may also beused without cross-linking.

It is so contemplated that the fluids of the present invention maycontain other materials besides the heteropolysaccharides eithercross-linked or not, the oxygenated dispersant and the aqueous medium.

If used as preferred, the alkaline medium may be an aqueous solution ofan alkali metal hydroxide such as sodium, potassium or lithiumhydroxide. Sodium hydroxide is to be preferred, and the amount ofalkaline medium employed may be sufiicient to provide a pH in the fluidfrom about 8.0 to about 10.0.

It is to be realized that where the oxygenated dispersant is acidic, asufficient amount of alkaline medium should be used to provide a pH ofabout 7 to 10.

The fluid of the present invention may contain other additives such asweighting agents, bactericides, gel forming materials and the like, allas set out more fully in U.S. Pat. No. 3,243,000.

It is desirable that the fluid of the present invention be prepared in acertain manner. Thus, the heteropolysaccharide in the amount given isadded to the oxygenated dispersant. Thus, from about 0.25 to about 1.0percent by wt. of the heteropolysaccharide is added to about 1.0 to 30percent by wt. (both amounts based on the aqueous medium) of anoxygenated dispersant and the two components agitated or mixed for atime from about 0.25 to about 5 minutes to form a slurry which is thenmixed with the aqueous medium which may be sea water at a temperaturefrom about 28 F. to about F. for a time within the range of about 15 toabout 45 minutes to disperse the slurry in the aqueous medium.Optionally, an alkaline medium, preferably sodium hydroxide solutioncontaining about 0.5 to about 5.0 percent by wt. NaOH is added to theaqueous medium containing the dispersed slurry to provide a pH withinthe range of about 8.0 to about 10.0. Thereafter, the fluid may be usedas a drilling fluid in subfreezing or Arctic environments with optionaladdition of other agents such as bactericides, weighting agents,colloidal materials such as bentonite and the like.

DESCRIPTION OF THE PREFERRED MODES AND EMBODIMENTS In order toillustrate the present invention further, a typical drilling fluid whichpresents one example of a drilling liquid for use in a subfreezingenvironment is made up as follows:

Add 3.5 pounds of Kelzan Type AL (XC-Polymer with chrome-alumcross-linking agent) to 20 pounds ethylene glycol and mix lightly for 30seconds to form glycol-polymer slurry. The glycol-polymer slurry is thenadded to one 42-gallon barrel of cold sea water and agitated for 30minutes and thereafter an aqueous solution of sodium hydroxidecontaining the equivalent of one-third pound of sodium hydroxide isadded to the fluid to form a fluid of the present invention. This fluidhas the following properties:

pH 8.5-9.1 Freezing Point l5-20 F. Plastic Viscosity l5-20 cp.

Yield Point l5-20 Ib-IIOO sq. ft. Plastic Viscosity 5-l5 cp.

Mud Weight 9-105 p.p.g.

Freezing Point l5-20 F. or lower A fluid of these characteristics maycontain about 5 percent or more by wt. of ethylene glycol.

The heteropolysaccharide of the present invention may be suitably mixedby use of a mud gun or by introducing the components into a device whichgives a moderate to high rate of shear. The oxygenated dispersantheteropolysaccharide slurry should be mixed only lightly.

In an operation in accordance with the present invention, a well borewas drilled using a drilling fluid in which initially 25 barrels of mudwas mixed using 5.6 percent by wt. of ethylene glycol, 5.5 percent ofgel (bentonite) and 0.5 percent of chrome-alum cross-linkedheteropolysaccharide in an aqueous medium of sea water. The drillingfluid was circulated during the drilling operation with the result thatthe cuttings were carried out of the hole with the drilling fluid. Thedrilling operation was continued in which a slurry of about 3.5 poundsof chromium cross-linked heteropolysaccharide produced by Xanthomonascampestris polymer and about 20 pounds per barrel ethylene glycol wasemployed with sea water from the Beaufort Sea. Drilling operations wereconducted on an island in the Beaufort Sea and during the drillingoperations cores were taken at intervals. It was found during thedrilling operations that the well bore at times during the coringoperations would contain a considerable amount of gravel; however, oncirculation of the drilling mud of the present invention, the hole wascleaned out and the cuttings were recovered.

In these operations, the drilling fluid performed satisfactorily in thatgood hole cleaning was achieved and there was no problem of drilling inthe subfreezing well bore environment.

In short, the fluid of the present invention functioned in a desirablemanner in Arctic operations during drilling on an island in the BeaufortSea where temperatures in the well were as low as F.

The nature and objects of the present invention having been completelydescribed and illustrated and the best modes and embodimentscontemplated set forth what I wish to claim as new and useful and secureby Letters Patent is:

l. A method for drilling a well which comprises:

' a. rotating a drill bit to form a well bore;

b. circulating in said well bore a drilling fluid containing:

1 a major amount of an aqueous medium;

2. an amount of a heteropolysaccharide produced by the action of thegenus Xanthomonas on a carbohydrate within the range from about 0.05 toabout 5.0 percent by wt. of the aqueous medium; and

3. an amount of an oxygenated dispersant within the range of about 2.0to about 30 percent by wt. of the aqueous medium; and

c. recovering cuttings from said well bore.

2. A method in accordance with claim 1 in which the heteropolysaccharideis heteropolysaccharide produced by Xanthomonas campestris.

3. A method in accordance with claim 1 in which the well is drilled in asubfreezing environment.

4. A method in accordance with claim 3 in which the subfreezingenvironment includes permafrost.

5. A method in accordance with claim 3 in which the subfreezingenvironment is in the Arctic.

6. A method in accordance with claim 1 in which the aqueous medium issea water.

7. A method in accordance with claim 1 in which the aqueous medium isbrine.

8. A method in accordance with claim 1 in which the aqueous medium isfresh water.

9. A method in accordance with claim 1 in which the aqueous mediumcomprises a drilling mud.

10. A method in accordance with claim 1 in which the oxygenateddispersant is a polyhydric alcohol.

11. A method in accordance with claim 1 in which the oxygenateddispersant is ethylene glycol.

12. A method in accordance with claim 1 in which theheteropolysaccharide is further dispersed by the addition of an amountof an alkaline medium sufficient to provide a pH in said fluid withinthe range of about 8 to about l0.

13. A method in accordance with claim 12 in which theheteropolysaccharide is heteropolysaccharide produced by Xanthomonascampestris.

14. A method in accordance with claim 12 in which the alkaline medium isa solution of an alkali metal hydroxide.

15. A method in accordance with claim 1 in which theheteropolysaccharide is cross-linked with a polyvalent metal cationselected from Groups 111 through VIII of the Periodic Table.

16. A method in accordance with claim 1 in which theheteropolysaccharide is cross-linked.

17. A method in accordance with claim 1 in which theheteropolysaccharide is cross-linked with a trivalent chromium compound.

18. A method in accordance with claim 1 in which theheteropolysaccharide is cross-linked with chrome-alum.

19. A method in accordance with claim 1 in which:

a. the oxygenated dispersant is ethylene glycol;

b. the heteropolysaccharide is Xanthomonas campestris;

and

c. the aqueous medium comprises sea water.

20. A method in accordance with claim 19 in which theheteropolysaccharide is further dispersed by the addition of an amountof an alkaline medium sufficient to provide a pH in said fluid withinthe range of about 8 to about 10.

21. A method in accordance with claim 19 in which the fluid ismaintained at temperatures below 32 F.

22. A method in accordance with claim 1 in which theheteropolysaccharide is cross-linked.

2. A method in accordance with claim 1 in which the heteropolysaccharideis heteropolysaccharide produced by Xanthomonas campestris.
 2. an amountof a heteropolysaccharide produced by the action of the genusXanthomonas on a carbohydrate within the range from about 0.05 to about5.0 percent by wt. of the aqueous medium; and
 3. an amount of anoxygenated dispersant within the range of about 2.0 to about 30 percentby wt. of the aqueous medium; and c. recovering cuttings from said wellbore.
 3. A method in accordance with claim 1 in which the well isdrilled in a subfreezing environment.
 4. A method in accordance withclaim 3 in which the subfreezing environment includes permafrost.
 5. Amethod in accordance with claim 3 in which the subfreezing environmentis in the Arctic.
 6. A method in accordance with claim 1 in which theaqueous medium is sea water.
 7. A method in accordance with claim 1 inwhich the aqueous medium is brine.
 8. A method in accordance with claim1 in which the aqueous medium is fresh water.
 9. A method in accordancewith claim 1 in which the aqueous medium comprises a drilling mud.
 10. Amethod in accordance with claim 1 in which the oxygenated dispersant isa polyhydric alcohol.
 11. A method in accordance with claim 1 in whichthe oxygenated dispersant is ethylene glycol.
 12. A method in accordancewith claim 1 in which the heteropolysaccharide is further dispersed bythe addition of an amount of an alkaline medium sufficient to provide apH in said fluid within the range of about 8 to about
 10. 13. A methodin accordance with claim 12 in which the heteropolysaccharide isheteropolysaccharide produced by Xanthomonas campestris.
 14. A method inaccordance with claim 12 in which the alkaline medium is a solution ofan alkali metal hydroxide.
 15. A method in accordance with claim 1 inwhich the heteropolysaccharide is cross-linked with a polyvalent metalcation selected from Groups III through VIII of the Periodic Table. 16.A method in accordance with claim 1 in which the heteropolysaccharide iscross-linked.
 17. A method in accordance with claim 1 in which theheteropolysaccharide is cross-linked with a trivalent chromium compound.18. A method in accordance with claim 1 in which theheteropolysaccharide is cross-linked with chrome-alum.
 19. A method inaccordance with claim 1 in which: a. the oxygenated dispersant isethylene glycol; b. the heteropolysaccharide is Xanthomonas campestris;and c. the aqueous medium comprises sea water.
 20. A method inaccordance with claim 19 in which the heteropolysaccharide is furtherdispersed by the addition of an amount of an alkaline medium sufficientto provide a pH in said fluid within the range of about 8 to about 10.21. A method in accordance with claim 19 in which the fluid ismaintained at temperatures below 32* F.
 22. A method in accordance withclaim 1 in which the heteropolysaccharide is cross-linked.